The rare gases, i.e. krypton and xenon, exist in very small concentrations in the atmosphere. Xenon is found in the ambient air in a concentration of 0.087 parts per million (ppm) and krypton is found in the ambient air in a concentration of 1.14 ppm. Because of these very small concentrations, krypton and xenon can be economically produced from only very large cryogenic air separation plants. Since the demand for these rare gases is increasing, it is desirable to be able to produce economically krypton and xenon from any size cryogenic air separation plant, and not just the very large cryogenic air separation plants.
Accordingly, it is an object of this invention to provide a system which will facilitate the recovery of krypton and xenon from smaller as well as larger cryogenic air separation plants.
Cryogenic air separation plants which produce gaseous oxygen operate most efficiently at steady state conditions. Unfortunately the demand for oxygen produced from such a facility can fluctuate between periods of high demand and periods of low demand as often as every few minutes or hours. This may require that such cryogenic air separation plants operate in an inefficient manner for much of the time although a number of methods have been identified to minimize operating and capital costs to meet variable demand.
Accordingly, it is another object of this invention to provide a system whereby cryogenic air separation plants which produce gaseous oxygen, such as for delivery to a pipeline, may operate at efficient steady state conditions during both high and low demand periods.